unsalted butter, room temperature, cut into 8 pieces
egg white, for glazing
cream cheese, room temperature
grated lemon zest
sour cream, plus
sour cream, room temperature
fresh lemon juice
eggs, room temperature
- Preheat oven to 350*F. Lightly grease an 8" square baking pan with butter.
- For the base:.
- Process the flour and confectoner's sugar in a food processor for several seconds. Add the butter and process until the dough comes together, 20 to 30 seconds.
- Pat the dough gently over the bottom of prepared pan and about 1" up the sides. Glaze it with the egg white: Pour the egg white on the dough and tip the pan from side to side so the white spreads over the surface. Pour off the excess.
- Bake the base on the center oven rack until golden, about 25 minutes. Place the base in the refrigerator for about 15 minutes to cool completely. Keep on the oven.
- Meanwhile prepare the topping:.
- Using an electric mixer on medium high speed, cream the cream cheese, sugar, and lemon zest together in a medium bowl till light and fluffy, 2 to 3 minutes. Stop the mixer once or twice to scrape the bowl with a rubber spatula.
- Add the sour cream and lemon juice and beat the mixture on medium high speed until smooth, about 1 minute. Scrape the bowl.
- Add the eggs and vanilla and beat on medium high speed until smooth and creamy,about 10 seconds. Spread the topping evenly over the base.
- Bake the bars on the center oven rack until the top is slightly golden and a toothpick inserted in the center comes out dry, about 1 hour. If the topping bubbles up during baking, prick the bubbles with a toothpick or a thin knife.
- Allow the bars to cool completely on a rack. Cut them with the point of a thin sharp knife that is dipped in hot water and wiped dry before each cut.